623 research outputs found
Fermi surface of an important nano-sized metastable phase: AlLi
Nanoscale particles embedded in a metallic matrix are of considerable
interest as a route towards identifying and tailoring material properties. We
present a detailed investigation of the electronic structure, and in particular
the Fermi surface, of a nanoscale phase ( AlLi) that has so far been
inaccessible with conventional techniques, despite playing a key role in
determining the favorable material properties of the alloy (Al\nobreakdash-9
at. %\nobreakdash-Li). The ordered precipitates only form within the
stabilizing Al matrix and do not exist in the bulk; here, we take advantage of
the strong positron affinity of Li to directly probe the Fermi surface of
AlLi. Through comparison with band structure calculations, we demonstrate
that the positron uniquely probes these precipitates, and present a 'tuned'
Fermi surface for this elusive phase
A High-Resolution Compton Scattering Study of the Electron Momentum Density in Al
We report high-resolution Compton profiles (CP's) of Al along the three
principal symmetry directions at a photon energy of 59.38 keV, together with
corresponding highly accurate theoretical profiles obtained within the
local-density approximation (LDA) based band-theory framework. A good accord
between theory and experiment is found with respect to the overall shapes of
the CP's, their first and second derivatives, as well as the anisotropies in
the CP's defined as differences between pairs of various CP's. There are
however discrepancies in that, in comparison to the LDA predictions, the
measured profiles are lower at low momenta, show a Fermi cutoff which is
broader, and display a tail which is higher at momenta above the Fermi
momentum. A number of simple model calculations are carried out in order to
gain insight into the nature of the underlying 3D momentum density in Al, and
the role of the Fermi surface in inducing fine structure in the CP's. The
present results when compared with those on Li show clearly that the size of
discrepancies between theoretical and experimental CP's is markedly smaller in
Al than in Li. This indicates that, with increasing electron density, the
conventional picture of the electron gas becomes more representative of the
momentum density and that shortcomings of the LDA framework in describing the
electron correlation effects become less important.Comment: 7 pages, 6 figures, regular articl
Acoustic emission behavior of steel fibre reinforced concrete under bending
The present paper describes the acoustic emission (AE) behavior of concrete under four-point bending. Steel fibres of varying content were used as reinforcement in concrete slabs and their influence on the fracture process and the acoustic activity was investigated. The total acoustic emission (AE) activity was found to be directly proportional to the fibre content. Analysis revealed that particular AE parameters change monotonically with the progress of damage and can be used for the characterization of the failure process
A Basic Study on Temporal Parameter Estimation of Wheelchair Propulsion based on Measurement of Upper Limb Movements Using Inertial Sensors
Wheelchairs are the most widely used assistive
device to aid activities of daily living (ADL) for disabled
people. However, manual pushing of a wheelchair
frequently leads to overuse of upper extremities causing
shoulder pain and carpal tunnel syndrome. The purpose of
this study was to test a novel method of estimating temporal
parameters of wheelchair propulsion using inertial sensors.
In this paper, normalized coordinate values of the vector
defined on the upper arm were calculated from an inertial
sensor attached on the upper arm. The number of strokes
and push cycle timings including duration of propulsion and
recovery phases were estimated for steady state wheelchair
propulsion. This estimation was completed using a novel
vector-based approach and a previously published resultant
acceleration method; both were compared to timings
measured using the SmartWheel. Measurements were
performed on level and sloped surfaces with 10 able bodied
subjects. The vector-based method improved estimation of
the number of strokes when compared to the resultant
acceleration method. However, the push cycle was estimated
with better accuracy by the resultant acceleration method.
Therefore, a combination of the vector-based and the
resultant acceleration methods is proposed to ensure more
accurate estimation of temporal parameters. The results
suggest inertial sensors can be used to measure wheelchair
activity accurately and reliably
Monitoring bridge degradation using dynamic strain, acoustic emission and environmental data
This paper studies the long term structural behaviour of a Victorian railway viaduct under train loading and temperature variation. A multi-sensing, self-sustaining and remotely controlled data acquisition system combines fibre Bragg grating strain sensors with acoustic emission sensors for the study of both global dynamic deformation and local masonry deterioration. A statistical analysis of fibre Bragg grating signals reveals regions with permanent change in the dynamic deformation of the bridge over the last two years, whereas in other locations the deformation follows a seasonal cyclic pattern. In order to decouple changes in structural behaviour due to real mechanical damage from normal seasonal effect, the paper studies the ambient temperature effect on the dynamic deformation of the bridge, showing a clear linear dependence. In particular, when temperature increases, the dynamic strain due to train loading decreases uniformly in the longitudinal direction. In the transverse direction, where the thermal expansion is not constrained, the decrease is smaller. Decoupling damage from normal seasonal effect is of critical importance for the development of reliable early warning structural alert systems for infrastructure networks. The paper further studies local masonry deterioration at four critical location by combining data from the two sensing technologies: fibre optic and acoustic emission sensors.This work is being funded by the Lloydās Register Foundation, EPSRC and Innovate UK through the Data-Centric Engineering programme of the Alan Turing Institute and through the Cambridge Centre for Smart Infrastructure and Construction. Funding for the monitoring installation was provided by EPSRC under the Ref. EP/N021614/1 grant and by Innovate UK under the Ref. 920035 grant
A new double-layered kagome antiferromagnet ScFeGe
ScFeGe with the LiFeGe-type structure (space group
), which has a double-layered kagome lattice (18 site) of Fe
crystallographically equivalent to that of a well-known topological ferromagnet
FeSn, is newly found to be antiferromagnetic (AFM) with a high N\'eel
temperature of K, in contrast to the ferromagnetic
(FM) ground state previously proposed in a literature. Sc nuclear
magnetic resonance experiment revealed the absence of a hyperfine field at the
Sc site, providing microscopic evidence for the AFM state and indicating AFM
coupling between the bilayer kagome blocks. The stability of the AFM structure
under the assumption of FM intra-bilayer coupling is verified by DFT
calculations.Comment: 13 pages, 1 tables, 4 figure
Recommendation of RILEM TC 212-ACD: acousticemission and related NDE techniques for crack detectionand damage evaluation in concrete. Measurement method for acoustic emission signals in concrete
The text presented hereafter is a draft for general consideration
Recommendation of RILEM TC 212-ACD: acousticemission and related NDE techniques for crack detectionand damage evaluation in concrete.Test method for damage qualification of reinforced concrete beams by acousticemission
The text presented hereafter is a draft for general consideration
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